This report updates activity through March 2008. Our last overview of Ulawun (BGVN 32:02) reported little activity of note other than frequent ash plumes from March 2006 to January 2007. Typical activity at Ulawun has consisted of gentle emission of thin-to-thick white vapor from the summit Based on satellite imagery and information from the Rabaul Volcano Observatory (RVO), the Darwin VAAC reported that diffuse plumes from Ulawun drifted N on 28 April 2007. On 1 May, an ash plume rose to an altitude of 4 km and drifted W.

[On 29 May 2007, RVO reported thick white vapor; there were no audible noises or night glow.] The two N valley vents remained quiet. Seismicity was at a low to moderate level dominated by low-frequency earthquakes. Through May, between 500 and 1,265 low frequency events were recorded daily with the most recorded on 28 and 29 May.

Similar conditions continued through the end of 2007 with only minor incidental variation. On 6 June, the elevated characteristics of the forceful emissions of 28-29 May were repeated. The daily total number of low-frequency earthquakes fluctuated between 400 and 1,042 events with the highest numbers recorded on 24 June (1,032) and 8 August (1,042). A high-frequency earthquake was recorded on 1 August. On 3 September forceful emissions were recorded sending the vapor plume ~ 1 km above the summit before being blown SE. On 25 December, based on satellite imagery observations, the Darwin VAAC reported that an ash-and-steam plume from Ulawun drifted W.

Low levels of activity continued from January through March 2008. Emissions consisted of thin to thick white vapor and with no audible noises and no glow visible at night. Seismicity continued at moderate level dominated by low frequency volcanic earthquakes. Variable amounts of white fume were emitted, sometimes forcefully. The two N valley vents continued to remain quiet.

Geological Summary. The symmetrical basaltic-to-andesitic Ulawun stratovolcano is the highest volcano of the Bismarck arc, and one of Papua New Guinea's most frequently active. The volcano, also known as the Father, rises above the N coast of the island of New Britain across a low saddle NE of Bamus volcano, the South Son. The upper 1,000 m is unvegetated. A prominent E-W escarpment on the south may be the result of large-scale slumping. Satellitic cones occupy the NW and E flanks. A steep-walled valley cuts the NW side, and a flank lava-flow complex lies to the south of this valley. Historical eruptions date back to the beginning of the 18th century. Twentieth-century eruptions were mildly explosive until 1967, but after 1970 several larger eruptions produced lava flows and basaltic pyroclastic flows, greatly modifying the summit crater.

Information Contacts: Herman Patia, Rabaul Volcano Observatory (RVO), P. O. Box 386, Rabaul, Papua New Guinea; Darwin Volcanic Ash Advisory Centre (VAAC), Commonwealth Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); US Air Force Weather Agency (AFWA), Satellite Applications Branch, Offutt AFB, NE 68113-4039, USA; Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); James Mori, Disaster Prevention Research Institute, Kyoto University, Uji, Kyoto 611-0011, Japan (URL: http://eqh.dpri.kyoto-u.ac.jp/~mori/).